Windowed door for a cooking appliance

ABSTRACT

The present invention relates to a windowed door ( 4 ) for a cooking appliance ( 2 ), in particular a cooking oven. The windowed door ( 4 ) comprises a front plate ( 6 ) and at least one inner plate ( 22 ) facing a cooking chamber ( 30 ) of the cooking appliance ( 2 ), wherein the front plate ( 6 ) and the at least one inner plate ( 22 ) each provide a glass pane ( 8, 24 ) and are connected with each other by at least lateral frame parts ( 26 ) to establish an air channel ( 11 ) from at least one air inlet opening ( 13 ) arranged at the bottom of the door ( 4 ) through a hollow space ( 28 ) between the glass pane ( 8 ) of the front plate ( 6 ) and the glass pane ( 24 ) of the at least one inner plate ( 22 ) to at least one air outlet opening ( 14 ) arranged at the top of the door ( 4 ). To regulate the air flow through the air channel ( 11 ) at least one automatically moveable closure device ( 40 ) is provided which permits the regulation of the air flow by changing the cross-section of at least one air passage aperture ( 29 ) within ( 64 ) or at the end ( 62 ) or at the beginning ( 60 ) of the air channel ( 11 ).

The present application is directed to a windowed door for a cookingappliance, in particular to a windowed door for a cooking oven. Moreoverthe present application is directed to a cooking appliance with such awindowed door.

To be able to observe food while being cooked in a cooking chamber of acooking appliance—such as ovens, steamers, microwaves, grills orcombinations thereof for example—the cooking chamber is usually closedwith a windowed door. Thereby it is no longer necessary to open thecooking appliance to check the cooking process and a stable cookingtemperature can be maintained.

A windowed door for a pyrolytic self-cleaning oven is for example knownfrom U.S. Pat. No. 3,760,792 A. The door of the oven includes a coolingair channel between two adjacent glass panes with air inlet means alongthe bottom of the door and air outlet means along the top of the door. Amanually operable hollow shutter is mounted for movement within the airchannel between an open position hidden within the door to permitviewing through the window and a closed position for covering the glasspane for both restricting the radiation of heat through the windowopenings and forcing the cooling air to pass through the shutter. Bychanging of the position of the shutter from the open to the closedposition the air inlet means are opened. Such a cooling with air duringa self-cleaning operation of the oven is necessary to reduce thetemperature at the outer side of the door for avoiding injuries of auser by contact with the outer side of the door. Although with such ashutter the temperature on the outer side of the door can be reduced, ithas turned out that users sometimes forget to change the position of theshutter and thereby opening of the air inlet means before activating theself-cleaning operation of the oven and therefore the danger of injuriesof a user cannot be reliably excluded.

From DE 103 49 313 A1 a cooking oven with a windowed door is known whichprovides a front plate and a rear plate which are connected with eachother by lateral U-shaped carriers. To avoid injuries of a user causedby high temperatures on the outer side of the front plate the hollowspace between the plates can be cooled by external air flowing frombottom to top of the door and by passing through openings in thecarriers in the upper part of the door wherein these openings aresurrounded by mechanical barriers integrated within the carriers toprevent air warmed up by the flange of the muffle of the oven fromflowing into the hollow space. However, in operation it has turned outthat moisture can be drawn within the hollow space due to permanentlyflow of external air through the hollow space which can cause fogging ofthe glass panes of the front plate and rear plate.

It is an object of the present invention to remove the problems andinconveniences observed with state of the art. In particular a windoweddoor for a cooking appliance with user friendly handling and/oreffecting a lower energy consumption of the cooking appliance shall beprovided. Further a cooking appliance with such a windowed door shall beprovided.

This object is solved by claims 1 and 14. Embodiments in particularresult from dependent claims.

According to claim 1, a windowed door for a cooking appliance isprovided comprising a front plate and at least one inner plate facing acooking chamber of the cooking appliance, wherein the front plate andthe at least one inner plate each provide a glass pane and are connectedwith each other by at least lateral frame parts to establish an airchannel from at least one air inlet opening arranged at the bottom or inat least one lateral side of the door through a hollow space between theglass pane of the front plate and the glass pane of the at least oneinner plate to at least one air outlet opening arranged at the top ofthe door and wherein at least one automatically moveable closure deviceis provided which permits the regulation of air flow through the airchannel by changing the cross-section of at least one air passageaperture within or at the end or at the beginning of the air channel.

Expediently the glass panes of the front plate and the inner plate arealigned to each other to be able to look into the cooking chamber of thecooking appliance. The front plate can provide a frame with a windowopening in which the glass pane is inserted or can be built by the glasspane itself. The same applies for the at least one inner plate.

The front plate and the at least one inner plate can be connected witheach other not only by lateral frame parts, but by a U-shaped or aperipheral frame, too, which include such lateral frame parts.Furthermore, the lateral frame parts or the U-shaped frame or theperipheral frame for connection of the plates can be provided in theregion of the outer edges of the plates or offset inwards with respectto the outer edges. Further on, the plates can be connected with eachother only or additionally by at least lateral frame parts or a U-shapedframe or a peripheral frame in the region of the glass panes of theplates. The general function of the lateral frame parts or the U-shapedframe or the peripheral frame is to keep the front plate and the atleast one inner plate fixed to each other. The front plate, the at leastone inner plate together with the lateral frame parts or the U-shapedframe or the peripheral frame is hereinafter referred to “doormechanical structure”. Especially in the case of use of a U-shaped framethe upper part of the windowed door can be closed by a door cap to builda kind of peripheral frame comprising the U-shaped frame and the doorcap.

By connection of the outer plate and the at least one inner plate bylateral frame parts the glass panes of outer plate and at least oneinner plate are spaced from one another which results in formation of ahollow space between the plates or rather the panes. To establish an airflow through the hollow space between the glass panes of the front plateand the at least one inner plate in case of a peripheral frame at leastone air passage aperture for air inlet and at least one air passageaperture for air outlet have to be provided in the frame. In case of aU-shaped frame in combination with a door cap at least one air passageaperture for air inlet has to be provided in the base of the U-shapedframe and at least one air passage aperture for air outlet has to beprovided in the door cap or has to be built between door mechanicalstructure and door cap. If only lateral frame parts are provided theside areas of the hollow space not limited by the lateral frame partscan serve as air passage apertures for air inlet and air outlet and canserve as air inlet opening and air outlet opening. To establish acontinuous air channel and especially an air flow from at least one airinlet opening to at least one air outlet opening thereby passing thehollow space between the glass panes it is necessary that in case ofhorizontal or inclined frame parts or other horizontal or inclinedsupports or struts within the door mechanical structure and situatedbetween at least one air inlet opening and at least one air outletopening these are provided with at least one air passage aperture. Thisor these air passage apertures can serve as air inlet opening and/or airoutlet opening, too, and can be situated at the beginning of the airchannel, that means near or at the at least one air inlet opening, orsomewhere within the air channel—for example if the glass panes arefixed to each other with additional lateral frame parts or an additionalU-shaped or peripheral frame—at the end of the air channel, that meansnear or at the end of the at least one air outlet opening, dependent onthe individual design of the door mechanical structure.

The at least one air inlet opening or the at least one air outletopening or the at least one air passage aperture can be constituted by aslot-like opening. Expediently more than one air inlet opening and/orair outlet opening are provided to provide a homogeneous air flowthrough the door and in particular through the hollow space between thefront plate and the at least one inner plate. Especially the at leastone air inlet opening at the bottom of the door is situated in the lowerthird of the windowed door, or in at least one lateral side of thewindowed door and the at least one air outlet opening at the top of thedoor is situated in the upper third of the windowed door to achieve agood cooling effect of the front plate of the door and in particular avertical air flow through the hollow space.

For instance, as mentioned before the at least one air passage aperturecan be constituted by the at least one air inlet opening, the at leastone air outlet opening or by an opening of the hollow space not limitedby the lateral frame parts.

The term “automatically moveable” shall mean that no direct manualinteraction with a user is necessary, user need not to effect directly amovement.

The invention is based on the recognition that a cooking appliance witha windowed door which provides an air channel between at least two glasspanes of the door for providing a permanent air flow through the hollowspace between the glass panes has an increased energy consumption incomparison to a cooking appliance with a windowed door which does notcomprise such an air channel.

Moreover, the invention is based on the consideration that cooling of awindowed door is usually only necessary when the cooking appliance isoperated at high temperatures, for example during a self-cleaningoperation or so-called pyrolytic cycle of the cooking appliance, whereasduring normal operation often only less or no cooling and in particularduring a preheating operation no cooling of the door is required becausethe door will not reach temperatures which could cause injuries to auser by contact with the outer side of the door.

The applicant has found that by providing an automatically moveableclosure device which permits the regulation of air flow through an airchannel within a windowed door by changing the cross-section of at leastone air passage aperture within or at the end or at the beginning of theair channel the air flow can be purposefully adapted to the operationmode of a cooking appliance. For example during a self-cleaningoperation of the cooking appliance which is accompanied with hightemperatures the closure device can provide that the cross-section ofthe at least one air passage aperture is completely permeable for air,whereas during normal operation the closure device provides at least apartial reduction of the cross-section of the at least one air passageaperture. Hereby the energy consumption of the cooking appliance can bepositively influenced, dependent on the operation mode of the cookingappliance the cross-section of the at least one air passage aperture ischangeable whereby energy loss because of unnecessary cooling of thewindowed door can be avoided. Further on, applicant has found that bysuch an automatically moving closure device no damages to the windoweddoor and/or a corresponding cooking appliance as well as injuries of theuser by unintentional contact with the door during operation of thecooking appliance at high temperatures will occur in comparison toclosure devices which require for example manual operation by a user foropening an air inlet opening—because in the latter case it cannot beexcluded that the user forgets to change the position of closure device.Because a windowed door with an automatically moveable closure devicerequires no explicit action of the user to induce or stop cooling of thewindowed door the handling of a cooking appliance with a windowed dooraccording to the invention is much more convenient and easier for theuser.

In embodiments of the windowed door, the at least one closure device isdesigned so that it can completely interrupt an air flow through thehollow space. This is advantageous because the energy consumption of acooking appliance during a preheating mode can be reduced because inthis mode no cooling of the windowed door and in particular of the frontplate is required, in particular it is favourable that the glass panesstay warm in this mode. Further on, if in the surrounding of the cookingappliance exists high air moisture or if the cooking appliance isoperated in a steam mode a complete interrupt of the air flow, inparticular at the beginning of the air channel or rather at the at leastone air inlet opening is favourable to avoid fogging of the glass panesdue to air moisture.

In embodiments of the windowed door, the at least one closure device isarranged within a door cap which is arranged at the top of the windoweddoor. The term “arranged within” shall mean that the closure device ispart of the door cap, however, the closure device does not have to becompletely within a housing of the door cap, but can build a part of thedoor cap, especially a replaceable part. The door cap itself can be aremovable, exchangeable part which at least partially covers the top ofthe windowed door. Such door caps are usually provided with at least oneair outlet opening, in particular with one or several slot-likeopenings. By providing the at least one closure device within the doorcap an easy exchange of the closure device in case of failure ispossible, even a complete change of the door cap can be considered. Byarrangement of the at least one closure device within the door cap theair flow through the air channel can be regulated by changing thecross-section of the at least one air outlet opening provided in thedoor cap. However, dependent on the design of the door cap and the atleast one closure device the cross-section of the hollow space betweenfront plate and at least one inner plate could be changed, too.

In embodiments of the windowed door, the at least one closure device isarranged between the front plate and the at least one inner plate. Theterm “between the plates” shall mean that the closure device can bearranged within the door mechanical structure of the windowed door, inparticular in such cases in which the at least one inner plate is therear plate of the windowed door. The arrangement of the at least oneclosure device can be in longitudinal direction or in cross directionwith respect to the front plate and the at least one inner plate.Preferably the at least one closure device is arranged at leastpartially above or beyond the glass panes of the front plate and the atleast one inner plate, whereby an upper or lower opening of the hollowspace between the glass panes can be regarded as the at least one airpassage aperture whose cross-section can be changed with help of the atleast one closure device.

In embodiments of the windowed door, the at least one closure device isin direct contact with the front plate or the at least one inner platewhen interrupting the air flow through the hollow space. The term“direct contact” shall include a contact with a sealing provided at thefront plate or at the at least one inner plate, too. It is especiallyadvantageous if the at least one closure device is in direct contactwith the front plate as well as with the at least one inner plate and isarranged above or beyond an opening of the hollow space. Thereby it canbe ensured that a reliable closure of the opening and thus aninterruption of an air flow through the hollow space can be achieved.

In embodiments of the windowed door, between the front plate and the atleast one inner plate at least one further plate comprising a glass paneis arranged. Advantageously, the at least one inner plate constitutesthe rear plate of the windowed door. To achieve a better insulationeffect of the cooking chamber of a cooking appliance which is closedwith a windowed door it is advantageous to provide multiple-glazing.Loss of heat and thus energy consumption of the cooking appliance can bereduced. It is also possible that front plate or rear plate or anyintermediate plates of a windowed door do not only comprise a singleglass pane, but a—in particular integral—subunit of several glass panes.

In embodiments of the windowed door, the at least one closure device isdesigned to carry out a horizontal movement to regulate the air flowthrough the hollow space. In particular by an arrangement of the closuredevice between the front plate and the at least one inner plate and/orabove or beyond an opening of the hollow space with a horizontalmovement the cross-section of the opening can be easily progressively orgradually changed.

In embodiments of the windowed door, the at least one automaticallymoveable closure device comprises at least one shape memory alloyelement designed to change the cross-section of the at least one airpassage aperture by moving of a cover element.

The cover element is preferably adapted to fully cover the cross-sectionof the at least one air passage aperture. Expediently the cover elementis movable in three mutually orthogonal directions.

The shape memory alloy element can be made from a copper-aluminum-nickelor a nickel-titanium alloy. Shape memory alloy elements have the abilityto return to a previously defined shape or size when subjected to anappropriate thermal procedure. Generally these materials can beplastically deformed at relatively low temperature and upon exposure tohigher temperature they return to their shape prior to the deformation.Shape memory alloys can have different shape memory effects, a so-called“one-way memory effect” and a so-called “two-way memory effect”. Theone-way memory effect can be described as follows: When the shape memoryalloy is in its cold state the metal can be bent or stretched and willhold those shapes until heated above a transition temperature. Uponheating the shape changes to its original. When the metal cools again,it will remain in the hot shape, until deformed again. The two-waymemory effect is the effect that the material remembers two differentshapes: one at low temperatures and one at high temperatures. In otherwords: A material that shows a shape memory effect during both heatingand cooling is called two-way shape memory. To achieve this the materialhas to be “trained” to “remember” its shape in the deformedlow-temperature condition.

The shape memory alloy element can be designed for example as strip,wire, spring, lamella, fin or vane. To be able to withstand more than10.000 movement cycles and/or deformation cycles a thickness of at least0.1 mm of the shape memory alloy element is favourable. In particular athickness of the shape memory alloy element of 0.1 to 1.2 mm isadvantageous.

Further on, it is favourable if the shape memory alloy element can carryout a stroke in a range of 1 to 25 mm. With a stroke in this range achange of a cross-section of the at least one air passage aperture withthe cover element with an ascertainable change of cooling of thewindowed door can be realized.

In one embodiment the shape memory alloy element is designed to cause amovement of the cover element at a predefined temperature, in particularat a temperature within a temperature range of 40° C. to 100° C. Forexample the shape memory alloy can be designed to return to its originalshape at a temperature of 80° C. That means, when the shape memory alloyelement reaches this temperature it will return to its original shapeand provide a movement of the cover element whereby a cross-section ofthe at least one air passage aperture can be changed, in particular canbe increased. To be able to change the size of the cross-section of theat least one air passage aperture step-by-step the at least oneautomatically moveable closure device can be provided with more than oneshape memory alloy element which can cause different strokes or lengthsof movement of the cover element at different predefined temperatures.For instance three shape memory alloy elements with different transitiontemperatures, for example 60° C., 80° C. and 100° C. could be providedwhich lead to different grades of movement of the cover element, forexample 5 mm, 10 mm and 15 mm.

In another embodiment the shape memory alloy element is designed tocause a progressive movement of the cover element, in particulardependent on the temperature change of air within the air channel.Thereby a progressive change of the cross-section of the at least oneair passage opening can be achieved, which allows a very good adjustmentof the air cooling effect of the windowed door. For example with a shapememory element providing a “two-way memory effect” at 60° C. and 80° C.a progressive shape modification or rather a progressive movement withinthis temperature range is possible. At a temperature of 70° C. thatshape memory element can be in an intermediate position for example,that means the shape memory element will have a shape between its shapeat 60° C. and its shape at 80° C. In other words, a movement or shapemodification of the shape memory element between a starting temperature(first shape) and a final temperature (second shape) will occurprogressively. If final or target temperature is not completely reachedshape memory element will have a shape between first and second shape.If temperature of shape memory element is further increased to finaltemperature shape memory element will reach its second shape, however ifshape memory element cools down again to starting temperature shapememory element will return from its intermediate shape to its firstshape.

In embodiments the at least one automatically moving closure devicecomprises at least one return member designed to bring back the shapememory alloy element into an initial shape after a warming up processfollowed by a cooling down process of the shape memory alloy element. Tobe able to repeatedly use a shape memory alloy element which comprises aone-way memory effect as an actuator a return member has to be providedwith which the shape memory alloy element can be brought back from itsoriginal shape to its initial, deformed shape after being heated to atemperature above its transition temperature. The return member can be aspring, in particular a coil spring or flat spring.

In embodiments the shape modification of the shape memory alloy elementis caused by heating of the shape memory alloy element via radiationheat emanating of the cooking chamber of the cooking appliance or viaJoule heating or via induction heating. A shape modification of a shapememory alloy element which can be induced by radiation heat, inparticular radiation heat emanating of the cooking chamber of thecooking appliance has the advantage that no further components withwhich a heating of the shape memory alloy element can be effected arerequired, whereby the closure device can be realized compact andlight-weight. A shape modification of a shape memory alloy element whichcan be induced by Joule heating by providing an electric current flowthrough the shape memory alloy element as well as a shape modificationof a shape memory alloy element which can be induced via inductionheating allows a precise control of the shape memory alloy element andespecially a precise control of the stroke that the shape memory alloyelement will perform, whereby the amount of change of the cross-sectionof the at least one air passage aperture can be adjusted.

In particular, the cover element is essentially made from metal orplastic. A cover element made from metal, for example steel, has theadvantage that it can withstand high temperatures and does not suffermaterial fatigue or deformation despite repeated large temperaturechanges. A cover element made from plastic has the advantage that itprovides a lower weight in comparison to a cover element made from metaland therefore not so much force to move the cover element is required,that means with even a less powerful closure device a reliable movementof the cover element can be realized. The cover element can be made froma combination of metal or plastic, too, to make use of the advantages ofboth materials. Also a cover element made from a composite material ispossible because such materials can for example withstand hightemperatures and exhibit a certain flexibility which can ensure areliable sealing of the cross-section of the at least one air passageaperture if required.

According to claim 14, a cooking appliance, in particular a cookingoven, is provided. The cooking appliance comprises a windowed dooraccording to any embodiment and configuration as set out above. As toadvantages, reference is made to the description above.

In embodiments of the cooking appliance, the cooking appliance providesa first and a second channel which are placed one above the other andwherein the first channel is arranged above the housing of a cookingchamber and the second channel is arranged beyond a control unit of thecooking appliance. Further on, a cooling fan is arranged at an areawhere the first and second channel are in operative connection with eachother to provide an air flow of air entering into the at least one airinlet opening, passing through the hollow space and then escaping viathe at least one air outlet opening, the first channel and the secondchannel. Hereby the air entering the windowed door through the at leastone air inlet opening cannot only be used for cooling the door and inparticular its front plate, but additionally for cooling the controlunit. Thus malfunction or failure of electronic components of controlunit or in particular electronic control mechanisms arranged above thehousing of the cooking chamber due to strong heat loads—for exampleduring a self-cleaning operation of the cooking appliance with hightemperatures within the cooking chamber—can be avoided.

As to advantages and advantageous effects of the windowed door and thecooking appliance further reference is made to the description above andbelow.

Preferred embodiments of the invention will now be described inconnection with the enclosed figures, in which:

FIG. 1a shows a perspective view of a cooking appliance,

FIG. 1b shows a fragmentary view from below of the windowed door of thecooking appliance of FIG. 1 a,

FIG. 2 is a fragmentary sectional view of the windowed door of thecooking appliance of FIG. 1a taken substantially along line II-II,

FIG. 3 is a fragmentary sectional view of the cooking appliance of FIG.1a taken substantially along line III-III with a position of a closuredevice of the windowed door allowing an air flow through the windoweddoor,

FIG. 4 is a fragmentary sectional view of the cooking appliance of FIG.1a taken substantially with a little parallel offset along line III-IIIwith a position of the closure device of the windowed door interruptingan air flow through the windowed door,

FIG. 5 shows a fragmentary sectional view of the windowed door of thecooking appliance of FIG. 1 taken substantially along line V-V of FIG.3,

FIG. 6 shows a fragmentary sectional view of the windowed door of thecooking appliance of FIG. 1a taken substantially along line VI-VI ofFIG. 4,

FIG. 7 shows a sectional view of the windowed door of the cookingappliance of FIG. 1a taken substantially along line V-V of FIG. 3providing an alternative configuration of a closure device,

FIG. 8 shows a sectional view of the windowed door of the cookingappliance of FIG. 1a taken substantially along line VI-VI of FIG. 7providing an alternative configuration of a closure device,

FIG. 9 shows a side view of the windowed door of the cooking applianceof FIG. 1a with a position of the closure device of the windowed doorallowing an air flow through the windowed door, and

FIG. 10 shows a side view of the windowed door of the cooking applianceof FIG. 1a with a position of the closure device of the windowed doorinterrupting an air flow through the windowed door.

Note, that the windowed door and the cooking appliance will be describedonly as far as is necessary for covering the invention.

FIG. 1a shows a perspective view of a cooking appliance 2, present acooking oven. The cooking appliance 2 comprises a windowed door 4. Thefront plate 6 of the windowed door 4 comprises a glass pane 8 and ahandle 10. The windowed door 4 is furnished with a removable or ratherexchangeable door cap 12 which is situated at the top of the windoweddoor. Present only the upper side of the door cap 12 is visible in FIG.1a , the rest of the door cap 12 is obscured by the front plate 6.Further on, the cooking appliance 2 comprises a control unit 18 with anoperating panel 19 with a user display 20 and adjustment knobs 21. Atthe bottom side of the windowed door 4—see FIG. 1b —one or more airinlet openings 13 in the form of elongated slots are provided. Arrow 15indicates cold air entering the air inlet openings 13 of the windoweddoor 4 and arrow 16 indicates hot air escaping from the cookingappliance 2 in the region of an opening between operating panel 19 andtop of the windowed door 4 built by a recess 17 provided at the top ofthe windowed door 4.

In FIG. 2 it can be seen that the windowed door 4 comprises an innerplate 22 which builds the rear plate of the windowed door 4. Inner plate22 comprises a glass pane 24, too. Inner plate 22 and front plate 6 areconnected with each other by a U-shaped frame 25 including lateral frameparts 26 and thereby define a hollow space 28 between them. This hollowspace 28 constitutes an air passage aperture 29 with a cross-sectiondefined by the distance of the in parallel arranged lateral frame parts26 and the distance of the parallel arranged front plate 6 and innerplate 22 or rather glass pane 8 and glass pane 24. To achieve a betterinsulation of the cooking chamber 30, surrounded by housing 31, of thecooking appliance 2 two further inner plates or intermediate plates 32,34 comprising glass panes 36, 38 are provided between front plate 6 andinner plate 22.

FIG. 3 shows a fragmentary sectional view of the cooking appliance 2 ofFIG. 1 taken substantially along line III-III. The door cap 12 whichcovers the top of the windowed door 4 comprises a closure device 40 withwhich the cross-section of an air passage aperture 29, present thecross-section of the hollow space 28, of an air channel 11 between theair inlet openings 13 at the bottom side of the windowed door 4 and anair outlet opening 14 of the windowed door 4 and passing through thehollow space 28 between front plate 6 and inner plate 22—or rather glasspane 8 and glass pane 24—can be changed or rather regulated. Present theair channel 11 begins at the air inlet openings 13, indicated byreference numeral 60, runs through the hollow space 28 between frontplate 6 and inner plate 22 and ends at air outlet opening 14, indicatedby reference numeral 62 (see also FIG. 1b , FIG. 9 and FIG. 10). Theslot-like air outlet opening 14 is built by a recess between door cap 12and inner plate 22. However, it is possible that the closure device 40or rather its housing 41 is not an integral part of the door cap 12, butis directly mounted within the door mechanical structure of the windoweddoor 4, too, that means closure device 40 could be arranged and fixedbetween front plate 6 and inner plate 22, especially in cases where thewindowed door 4 does not comprise a door cap 12, but for example aperipheral frame. One longitudinal side of the closure device 40 can bein contact with or fixed to the inner side of the front plate 6 orpresent to a longitudinal side of the door cap 12. The both transversesides of the closure device 40 extend along the top side of the frameparts 26. The closure device 40 is provided with an automaticallymoveable cover element 42 in form of a piston-shaped or hooded-shapedslider element which is movable along two lateral guide rails whichextend along the top side of the frame parts 26. Closure device 40itself and cover element 42 are essentially made from light-weightplastic material. However, the use of other materials is possible, too.The cover element 42 is designed in such a manner that it can carry outa stroke motion in horizontal direction, in the present case the coverelement 42 can make a linear movement in a direction perpendicular tothe area of the front plate 6 towards the inner plate 22. Dependent onthe stroke of the closure device 40 or rather the cover element 42 thetransversal length of the closure device 40 and hereby the cross-sectionof the air passage aperture 29, the hollow space 28, or rather the airflow between the glass panes 8, 24 can be varied.

As can be seen in FIG. 5 the closure device 40 comprises two shapememory alloy elements 44 made from a nickel-titanium alloy in form ofcoil springs with a thickness of 1 mm with which the cover element 42can be moved automatically. In other words, the shape memory alloyelements 44 serve as actuators for the cover element 42. The shapememory alloy elements 44 establish an operative connection betweenhousing 41 of closure device 40 and its closure element 42. Note,because in FIG. 5 only a fragmentary sectional view of the windowed door4 is shown only one of the shape memory alloy elements 44 andcorresponding return member 46 is visible. The non-visible shape memoryalloy element 44 and its corresponding return member 46 are arrangedsymmetrically in the other lateral end portion of the closure device 40.In its cold state the shape memory alloy elements 44 are impressed adeformation, present a deformation which provides a stretching of theshape memory alloy elements 44 induced by a spring force of returnmembers 46 in form of coil springs (see FIGS. 4 and 6, too). The shapememory alloy elements 44 comprise a “one-way memory effect”, if they arewarmed up to their transition temperature of 80° C. due to the increaseof temperature of air within the hollow space 28 caused by radiationheat emanating from the cooking chamber 30 they start to return to theirinitial, non-deformed shape. The shape memory alloy elements 44 are“trained” to progressively return to their initial shape with anincrease of temperature starting from their transition temperature of80° C. to a temperature up to 150° C. That means the cover element 42will start to make a stroke motion at 80° C. and a maximum stroke willbe reached at a temperature of 150° C. In the present case shape memoryalloy elements 44 and return members 46 are designed to enable a strokemotion of up to 25 mm. Dependent on the design of the shape memory alloyelements 44 and corresponding return members 46, especially thicknessand length, a larger stroke motion is possible. Instead of placing twoshape memory alloy elements 44 and corresponding return members 46symmetrically in the area of the lateral end portions of the closuredevice 40 or rather the cover element 42 only one shape memory alloyelement 44 and corresponding return member 46 could be alternativelyprovided in the middle of the closure device 40 to provide a symmetricalshift of the cover element 42 along its entire length.

In FIG. 4 and FIG. 6 the closure device 40 is shown in its startingposition with the visible shape memory alloy element 44 in its deformedor cold state. In the starting position no air flow between the glasspanes 8, 24 is possible because the closure device 40 completelyinterrupts an air flow from the air inlet openings 13 through the airoutlet opening 14. Until the shape memory alloy elements 44 reach atemperature of 80° C. no air flow will occur, that means in a preheatingoperation of the cooking appliance 2 the glass panes 8, 24, 36, 38 willstay warm and will not actively cooled by air because the hollow space28 is not permeable for air due to the position of the cover element 42.Only a warm air flow along the side of the glass pane 24 facing thecooking chamber 30 which emanates from the cooking chamber 30 ispossible as indicated by arrow 50. If the shape memory alloy elements 44reach a temperature of 150° C. the cover element 42 will be in its endposition, in other words a further retraction of the cover element 42 isno more possible. In this position as can be seen in FIG. 3 and FIG. 5air can flow along the inner side of the glass pane 8 as indicated byarrow 52.

Air flow as indicated by arrows 50, 52 is lead along a first channel 54above the housing 31 of the cooking chamber 30 from the front side ofthe cooking appliance 2 to its back side where a cooling fan 56 isarranged. By means of this cooling fan 54 the air passing through thefirst channel 54 can be redirected into a second channel 58. The airflow passing through the second channel 58 can escape through the recess17 as indicated by arrow 16. As can be seen in FIG. 3 and FIG. 4 firstchannel 54 and second channel 58 are in connection with each other atthe rear of the cooking appliance 2, where the cooling fan 56 is fixed.The second channel 58 runs above the first channel 54 and is locatedbeyond the control unit 18. Hereby especially the air of air flowindicated by arrow 52 which is responsible for cooling of the inner sideof front plate 6 or rather glass pane 8 can be used for cooling of thecontrol unit 18, too. Thereby the risk of a failure of electroniccomponents of the control unit 18 can be reduced.

FIG. 7 and FIG. 8 differ only from FIG. 5 and FIG. 6 that they suggestthe use of another kind and arrangement of shape memory alloy element44′ and corresponding return members 46′ to move cover element 42.Present the closure device 40 comprises only one shape memory alloyelement 44′ made from a copper-aluminum-nickel alloy or anickel-titanium alloy in form of a metal strip with a thickness of 1 mmwhose middle part is fixed to the cover element 42 and whose ends arefixed to a side of a housing 41 of the closure device 40 which issituated opposite to an area of the cover element 42 which can changeits position due to movement of the shape memory element 44′. In itscold state the metal strip is impressed a deformation, present adeformation which provides a curved shape of the shape memory alloyelement 44′ induced by a spring force of two return members 46′ in formof coil springs (see FIG. 8). The return members 46′ are laterallyarranged beside the metal strip or rather the shape memory alloy element44′. The coil springs as well as the metal strip are in the sameoperative connection with the side of the housing 41 of the closuredevice 40 and the area of the cover element 42 opposite this side of thehousing 41 as aforementioned. The metal strip comprises a “one-waymemory effect” as described above with reference to the shape memoryalloy elements 44 in form of coils springs. If the metal strip is warmedup to its transition temperature the metal strip starts to return to itsinitial, non-deformed shape, present a straightened shape. FIG. 7 showsthe cover element 42 in its end position which allows air flow along theinner side of glass pane 8.

FIG. 9 and FIG. 10 show a side view of the windowed door 4 of thecooking appliance 2. The dotted arrow 66 schematically indicates the airflow between front plate 6 and inner plate 22. The beginning 60 of theair channel 11 in the lower part of the windowed door 4 is built by theair inlet openings 13 and the end 62 of the air channel 11 in the upperpart of the windowed door 4 is built by air outlet opening 14. Inalternative or in addition, air can enter from an air inlet opening 13in at least one lateral side of the windowed door 4, such as indicatedschematically in FIG. 9 and flow, in particular through the air channel11, to the air outlet opening 14 in the upper part of the windowed door4. It can be seen that in FIG. 9 the cover element 42 of theautomatically moveable closure device 40 is in its fully retractedposition or rather its end position. In this position air flow betweeninner side of glass pane 8 of front plate 6 and inner plate 22 or ratherglass pane 24 is possible, this is demonstrated by arrow 52 whichindicates the escaping air through air outlet opening 14. In FIG. 10 itcan be seen that the cover element 42 of the automatically moveableclosure device 40 is in its starting position. In this starting positionno air flow at all between glass panes 8 and 24 is possible because airoutlet opening 14 is fully closed or sealed by cover element 42 orrather its piston-shaped or hooded-shaped slider element.

It has turned out that the energy consumption of a cooking appliance 2provided with such a windowed door 4 with an automatically moveableclosure device 40 can be reduced of about 10 to 20 Wh without risk ofhigh temperatures at the front plate 6 during normal operation incomparison to cooking appliances without such a door, in particularbecause the time for preheating of the cooking appliance 2 can bereduced. Moreover, especially during a self-cleaning operation of thecooking appliance 2 high temperatures at the outer side of front plate 6and thus injuries of an user are avoidable, whereas food leftovers atthe inner side of inner plate 22 are still easily removable.Furthermore, during a steaming operation especially fogging of the innerside of the glass pane 8 is avoidable, too.

Instead of arranging the closure device 40 above the glass panes 8, 22,36, 38 an arrangement beyond would be possible, too. Dependent on thedesign of the windowed door 4 and its glass panes 8, 24 an arrangementwithin air channel, for example at position 64, might be possible. Alsoan arrangement next to the air inlet openings 13 or air outlet opening14 to change the cross-section of these openings could be considered.Furthermore, instead of providing only one closure device 40 severalclosure devices could be provided, too, and/or one or more shape memoryalloy elements 44, 44′ and corresponding return members 46, 46′ could beused for moving the cover element 42. A use of a shape memory alloyelement 44, 44′ with which step-by-step movements of the cover element42 are possible could be also considered.

LIST OF REFERENCE NUMERALS

-   2 cooking appliance-   4 windowed door-   6 front plate-   8 glass pane of 6-   10 handle-   12 door cap-   13 air inlet opening-   14 air outlet opening-   15 arrow, indicating entering external cold air-   16 arrow, indicating escaping hot air-   17 recess at top of the windowed door 4-   18 control unit-   19 operation panel-   20 user display-   21 adjustment knobs-   22 inner plate-   24 glass pane of 22-   25 U-shaped frame-   26 lateral frame part of 25-   28 hollow space-   29 air passage aperture-   30 cooking chamber-   31 housing-   32 intermediate plate-   34 glass plane of 32-   36 intermediate plate-   38 glass pane of 36-   40 closure device-   41 housing of closure device 40-   42 cover element-   44, 44′ shape memory alloy element-   46, 46′ return member-   50 arrow, indicating air flow emanating from the cooking chamber-   52 arrow, indicating air flow passing through the hollow space 28    and escaping through air outlet opening 14-   54 first channel-   56 cooling fan-   58 second channel-   60 beginning of air channel 11-   62 end of air channel 11-   64 position between beginning 60 and end 62-   66 arrow, indicating air flow between beginning 60 and end 62

1. Windowed door for a cooking appliance comprising a front plate and atleast one inner plate facing a cooking chamber of the cooking appliance,wherein the front plate and the at least one inner plate each provide aglass pane and are connected with each other by at least lateral frameparts to establish an air channel from at least one air inlet openingarranged at the bottom or in at least one lateral side of the doorthrough a hollow space between the glass pane of the front plate and theglass pane of the at least one inner plate to at least one air outletopening arranged at the top of the door and wherein at least oneautomatically moveable closure device is provided which permits theregulation of air flow through the air channel by changing thecross-section of at least one air passage aperture within or at the endor at the beginning of the air channel.
 2. Windowed door according toclaim 1, wherein the at least one automatically moveable closure deviceis designed so that it can completely interrupt an air flow through thehollow space.
 3. Windowed door according to claim 1, wherein the atleast one automatically moveable closure device is arranged within adoor cap which is arranged at the top of the windowed door.
 4. Windoweddoor according to claim 1, wherein the at least one automaticallymoveable closure device is arranged between the front plate and the atleast one inner plate.
 5. Windowed door according to claim 1, whereinthe at least one automatically moveable closure device is in directcontact with front plate or the at least one inner plate wheninterrupting the air flow through the hollow space.
 6. Windowed dooraccording to claim 1, wherein between the front plate and the at leastone inner plate at least one further plate comprising a glass pane isarranged.
 7. Windowed door according to claim 1, wherein the at leastone automatically moveable closure device is designed to carry out ahorizontal movement to regulate the air flow through the hollow space.8. Windowed door according to claim 1, wherein the at least oneautomatically moveable closure device comprises at least one shapememory alloy element designed to change the cross-section of the atleast one air passage aperture by moving of a cover element.
 9. Windoweddoor according to claim 8, wherein the shape memory alloy element isdesigned to cause a movement of the cover element at a predefinedtemperature.
 10. Windowed door according to claim 8, wherein the shapememory alloy element is designed to cause a progressive movement of thecover element dependent on the temperature change of air within the airchannel.
 11. Windowed door according to claim 8, wherein the at leastone automatically moveable closure device comprises at least one returnmember designed to bring back the shape memory alloy element into aninitial shape after a warming up process followed by a cooling downprocess of the shape memory alloy element.
 12. Windowed door accordingto claim 8, wherein the a shape modification of the shape memory alloyelement is caused by heating of the shape memory alloy element viaradiation heat emanating of the cooking chamber of the cooking applianceor via Joule heating or via induction heating.
 13. Windowed dooraccording to claim 8, wherein the cover element is essentially made frommetal or plastic.
 14. Cooking appliance comprising a windowed dooraccording to claim
 1. 15. Cooking appliance according to claim 14,wherein the cooking appliance provides a) a first and a second channelwhich are placed one above the other and wherein the first channel isarranged above the housing of a cooking chamber and the second channelis arranged beyond a control unit of the cooking appliance, and b) acooling fan arranged at an area where the first and second channel arein operative connection with each other to provide an air flow of airentering into the at least one air inlet opening, passing through thehollow space and then escaping via the at least one air outlet opening,the first channel and the second channel.
 16. Windowed door according toclaim 9, said predefined temperature being within a temperature range of40° C. to 100° C.